In a conventional liquid crystal display, the display has been performed in the twisted nematic (TN) mode or in the super twisted nematic (STN) mode, in which both a first substrate and a second substrate are typically provided with respective electrodes for driving a liquid crystal and in which an electric field normal to the substrates is applied to the liquid crystal.
However, the mode using multiplex driving for the liquid crystal display of a simple matrix configuration results in a reduction in contrast or in a reduction in the speed of response varying as scanning lines are increased, and hence it becomes difficult to obtain a satisfactory contrast in the case of having about 200 scanning lines.
Thus, in order to eliminate such a deficiency, there tends to be employed an active-matrix mode liquid crystal panel, in which individual pixels are each provided with switching elements.
This active-matrix mode liquid crystal panel is largely classified into a three-terminal system using a thin-film transistor as the switching element and a two-terminal system using a non-linear resistance element. Of these, the two-terminal system is superior in that it is simple in structure and in its manufacturing process.
As this two-terminal system there have been developed a diode type, a varistor type, an MIM (Metal-Insulator-Metal) type, etc.
Among them, the MIM type is characterized in that it is especially simple in structure and has a shortened manufacturing process.
Furthermore, the liquid crystal display panel needs a high density as well as a high definition, so that it is necessary to reduce the area occupied by the switching elements.
The means for achieving that high density and high definition include a photolithography technique and an etching technique which are micro-treatment techniques in the semiconductor manufacturing technique. However, even though this semiconductor manufacturing technique has been used, it is extremely difficult to perform the microtreatment over a larger area and to achieve a low cost.
Next, a structure of a switching element effective for an enlargement of area and in a reduction in cost will be described with reference to FIG. 13 which is a plan view illustrating an example of the conventional liquid crystal display, and to FIG. 14 which is a sectional view taken along a line J--J thereof.
This liquid crystal display, as shown in FIG. 14, comprises a first substrate 41 and a second substrate 46 which are made of a transparent material and are opposed to each other by way of plural spacers 52 located at a predetermined distance, with a liquid crystal 51 being sealed thereinbetween.
On the first substrate 41 there is disposed for each pixel part a lower electrode 42 serving as a first electrode extending from a signal electrode 53, on which lower electrode 42 is formed a non-linear resistive layer 43 by means of an anodization method.
Moreover, an upper electrode 44 serving as a second electrode is disposed on the non-linear resistive layer 43 in an overlapping manner, to constitute a non-linear resistance element 40.
The upper electrode 44 as shown in FIG. 13 extends from a transparent display electrode 45 on a pixel part by pixel part basis, the second electrode being constituted of the upper electrode 44 and the display electrode 45.
On the other hand, a surface of the second substrate 46 confronting the first substrate 41 is provided with a black matrix 47 formed over the entirety of a shaded region shown in FIG. 13, in order to prevent any leakage of light through gaps between the display electrodes 45 disposed on the first substrate 41. In other words, non-display areas are provided with the black matrices 47 serving as light-blocking sections.
Furthermore, by way of a protective film 48 made of an organic material to prevent a short circuit resulting from any contact with the black matrix 47, a transparent counter electrode 49 is disposed in the form of a belt as shown in FIG. 13 on the second substrate 46 in such a manner as to confront the display electrode 45 as shown in FIG. 14.
Also, in order to protect the non-linear resistance element 40, an insulating film 55 made of tantalum oxide is disposed on the first substrate 41 and an opening is formed by dry etching at the connection with an external circuit.
As treatment layers for orderly arranging molecules of the liquid crystal 51, alignment layers 50, 50 are then disposed on the first substrate 41 and the second substrate 46, respectively.
As shown in the plan view of FIG. 13, the signal electrode 53 and the display electrode 45 have an interval equal to a predetermined dimension d therebetween.
The display electrode 45 is placed with respect to the liquid crystal 51 so as to overlap the counter electrode 49 and becomes each pixel part in a matrix-like display region consisting of a plurality of signal electrodes 53 having the non-linear resistance elements 40 and of a plurality of counter electrodes 49.
By making use of a variation in transmittance of the liquid crystal 51 in the region between the display electrode 45 and a portion of the counter electrode 49 in which no black matrix 47 is formed, the liquid crystal display can execute a predetermined image display.
It is to be noted that in FIG. 13 dotted lines indicate the lower electrode 42, the signal electrode 53, the upper electrode 44 and the display electrode 45 on the first substrate 41, with the non-linear resistive layer 43, the protective film 48, the insulating film 55 and the alignment layer 50 being not shown, and that the black matrix 47 and the counter electrode 49 on the underside of the second substrate 46 are indicated by solid lines.
At the time of actual display, in such a liquid crystal display, an electric field is applied between the first substrate 41 and the second substrate 46 in the direction perpendicular to the substrates so that molecules of the liquid crystal are turned from an orientation parallel to the substrates to an orientation normal to the substrates, thereby performing the display image.
Thus, in the conventional liquid crystal display, the electrodes for driving the liquid crystal are formed on the first substrate and the second substrate, and an electric field in the direction perpendicular to the substrates is applied to the liquid crystal to allow the display action to be carried out.
For this reason, the conventional liquid crystal display has presented a greater so-called dependence of display quality on the visual field angle, in which the display quality such (as contrast) varies depending on the viewing angle.
Measures to improve such a dependence on the viewing angle include means for correcting a phase difference in the direction of the liquid crystal molecules by utilizing a retardation film and means to manage the orientation of the liquid crystal molecules.
However, the measures using the retardation film are less effective in improving the dependence on the visual field angle. It is also difficult for the measures to manage the orientation of the liquid crystal molecules to ensure a stabilized orientation.
To this end, as can be seen in, for example, Japanese Patent Pub. No. sho63-21907, a liquid crystal display panel has been developed in which on a first substrate having non-linear resistance elements formed thereon there are disposed comb-teeth type electrodes in pairs on a pixel by pixel basis, with a voltage being applied between the comb-teeth type electrodes to control the liquid crystal molecules to turn to the direction parallel to the substrates. Such a method of controlling the liquid crystal molecules is called the IPS (In-Plane-Switching) method.
This is simply described with reference to FIG. 15, which is a diagrammatic enlarged plan view showing a fragmentary region of the liquid crystal display panel using the comb-teeth type electrodes.
As shown in this diagram, a first comb-teeth type electrode 63 and a second comb-teeth type electrode 64 are placed at a certain distance on the first substrate on a pixel part by pixel part basis.
A variation in magnitude of a voltage applied between the first comb-teeth type electrode 63 and the second comb-teeth type electrode 64 results in a change in the direction of the major axes of liquid crystal molecules 61 of the liquid crystal sealed in between the first and second substrates.
In the case of using a liquid crystal material having a negative dielectric anisotropy, the liquid crystal molecules 61 are maintained in the state indicated by a solid line during the application of a voltage smaller than a threshold voltage. On the contrary, when a voltage larger than the threshold voltage is applied, the liquid crystal molecules 61 are turned in the direction indicated by an arrow A and remain at the position indicated by an imaginary line. The liquid crystal molecules 61 are almost never pre-tilted relative to the first substrate and move substantially parallel to the first substrate.
On both sides of this liquid crystal panel there are arranged polarizing plates in such a manner that the transmission axes orthogonally intersect each other and that the transmission axis of either polarizing plate is parallel to the major axes of the liquid crystal molecules 61. Then, by varying the voltage applied between the first comb-teeth type electrode 63 and the second comb-teeth type electrode 64, the orientation of the liquid crystal molecules 61 are turned to execute the display.
More specifically, when the liquid crystal molecules 61 lie at the position indicated by the solid line, incident polarized light advances intactly straight and is blocked by the polarizing plate on the exit side, resulting in a black display. On the contrary, when the liquid crystal molecules 61 turn to the position indicated by the imaginary line, the incident polarized light enters at an angle of about 45 degrees relative to the liquid crystal molecules 61 to cause a phase difference. A white display is thus obtained by setting the birefringence of the liquid crystal and the cell gap so that the phase difference becomes equal to half of the wavelength.
However, in the case of incorporating the means to provide this comb-teeth type electrode into the liquid crystal display having the non-linear resistance elements, the two types of electrodes, that is, the first comb-teeth type electrode 63 and the second comb-teeth type electrode 64 need to intersect each other on the first substrate. The intersection between these two electrodes must be carefully considered so as not to bring about any electrical short circuit between the two electrodes.
Although as a measure against this, it is conceivable to provide an insulating film at the intersection between the two electrodes on the first substrate, this method needs an increase in thickness of the insulating film, disadvantageously resulting in not only an increase in the number of the manufacturing steps but also in a complicated process.